The Oregon DOT has changed Superpave design gyration levels for mixes used on the state highway system. Beginning immediately, Oregon highway mixes will be designed at 4.0 percent air voids at 65, 80, and 100 gyrations. For highways with low truck volumes (ODOT Level 2), gyrations have been rolled back from 75 to 65. Mixes to support moderate truck traffic (ODOT Level 3) will be designed at 80 gyrations instead of 100. Interstate and other highways with heavy truck traffic (ODOT Level 4) will be built with mixes designed at 100 gyrations rather than 125.
These changes are based on research conducted as part of NCHRP 9-9(1). Researchers concluded that laboratory densities were on average 1.5 percent greater than in-place densities of mix subjected to truck traffic. Fewer gyrations are required in the laboratory to simulate the densification of Superpave mixes in the field. These changes may affect some projects that will be constructed in 2007 and will be fully implemented in the 2008 ODOT Standard Specifications.